This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-336191, filed Nov. 2, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an induction charge mirror effectively applicable to, for example, a digital micromirror device.
The digital micromirror device (DMD) is known as a spatial light modulator for controlling the micromirror by an electrostatic force.
Before explaining the features of a DMD structure, an explanation will be made below about one pixel (cell) of a spatial light modulator shown in U.S. Pat. No. 5,867,202 with reference to FIG. 1.
A hinge 101 supports a yoke 102. The yoke 102 is rotable about a fulcrum axis 105 of the hinge 101. A mirror 103 is attached by a pillar 104 to the upper surface of the yoke 102, noting that, for a clear understanding of the structure of the Figure, the mirror 103 and yoke 102 are shown in a separated way. In symmetric positions with the hinge 101 as a center, two fixed electrodes (referred to also as address electrodes), thought not appearing in the Figure, are arranged at those fixed positions at a lower surface side of the yoke 102.
A drive circuit, not shown, supplies a voltage between either one of the fixed electrodes and the yoke 102 to create an electrostatic force. By doing so, the yoke 102 is driven, so that it is tilted toward a left (L) rotation or a right (R) rotation direction. The tilting of the yoke 102 means a variation of a mirror angle.
The drive circuit selects either of a first tilting direction and a second tilting direction. At a rate of a first tilting direction select period and a second tilting direction select period, modulation is imparted to light reflected by the mirror. The hinge 101 has three functions:
(1) In order to construct the spatial light modulator, the hinge 101 fixes each pixel forming mirror 103 and yoke 102 to a predetermined position.
(2) The hinge 101 provides a fulcrum for transforming a linear direction electrostatic force generated between the mirror 103 and yoke 102, on one hand, and the fixed electrode, on the other hand, to a rotation motion.
(3) The hinge 101 serves as a conductor for imparting a predetermined potential to the mirror 103 and yoke 102.
The hinge 101 performs an important function and, in order to be made movable under a small electrostatic force by applying a lower voltage, a hinge of small stress is demanded. In this case, however, a longer mechanical service life is also demanded even if it is rotated a very large number of times. Further, even if there is a history difference between the number of rotations in one direction and the number of rotations in the other direction, there is also a demand that no hysteresis occur in the hinge stress.
The hinge requires a high degree of technology. In order to enhance an aperture rate of the spatial light modulator, a two-level complicated structure is provided with a mirror 103 of a wider area mounted to cover the yoke 102 and hinge 101. Therefore, various kinds of pillars are required and hence a very complicated microstructure is provided.
As evident from the above, it is necessary to use a high degree of process control on the material and shape in the manufacture of this device and a very high degree of manufacturing technique.
It is accordingly the object of the present invention to provide an induction charge mirror which makes a rotation mirror which is operated under an electrostatic force hinge-free and achieving a greater aperture rate in a simpler structure and the easiness with which it is manufactured.
In order to achieve the above-mentioned object of the present invention, there is provided an induction charge mirror comprising an insulating substrate; a space defined in an upper surface portion of the insulating material and surrounded at least its surface portion with an insulating material; a flat mirror conductor having an area smaller than a planar area of the space and tiltably set within the space; a transparent electrode surrounding the space and the upper side of the mirror conductor; first and second fixed electrodes arranged at a lower surface side of the space and situated opposite to each other relative to a position at which the area of the mirror conductor is bisected; means for normally applying a first potential to the transparent electrode; and means for alternately applying second and third potentials to the first and second fixed electrodes so as to switch the tilting angle of the mirror conductor.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.